1. Field of the Invention
The present invention relates a wireless unit adapted to a time division multiple access (hereinafter abbreviated as a "TDMA") for use in mobile communication, and more particularly to a TDMA wireless unit adapted to a frequency division duplex (hereinafter abbreviated to "FDD") method in which different frequencies are used in transmission and reception and to a dual mode wireless unit enabling one unit to use the FDD method and a time division duplex (hereinafter abbreviated to "TDD") method which performs separation of transmission and reception from each other by a time division manner.
Moreover, the present invention relates to a two-frequency band-pass filter, a two-frequency branching filter and a two-frequency combiner.
The present invention as well as relates to a voltage controlled oscillator with controllable frequency band capable of using at least two frequency bands by switching.
Furthermore, the present invention relates to a two-terminal to multi-common terminal matrix switch for switching flows of signals mainly in a high frequency circuit among two terminals and two or more common terminals.
2. Related Art of the Invention
In recent years mobile communication service, such as an automobile telephone, a ship telephone, an airplane telephone and a train telephone, has been desired. Thus, various communication systems have been suggested. A TDMA system, which is one of the foregoing suggested systems, is a system in which a plurality of mobile stations with respect to a base station mutually use the same frequency in a time division manner. Since the TDMA system has been disclosed in detail in, for example, "Digital Mobile Communication", issued by Kagaku Shinbunsha, supervised by Moriji Kuwahara, pp. 62 to 69, description of the TDMA system is omitted here.
A conventional TDMA wireless unit and employing the TDD system to separate transmission and reception from each other will now be described with reference to the drawing. FIG. 7 is a block diagram showing a conventional TDMA wireless unit adapted to the TDD system. Referring to FIG. 7, when a signal is received, 1895.15 MHz to 1917.95 MHz, which is the reception frequency fR for the subject station, is selected by a high-frequency band-pass filter 3, followed by being supplied to a high-frequency amplifier 4 through an antenna switch 2 connected to terminal 2r so that the received signal is amplified. Then, the selectivity of the amplified signal is further raised by a high-frequency band-pass filter 5, and then, by a converter 6, mixed with first local oscillation frequency fL1 of 1646.85 MHz to 1669.65 MHz from a first local oscillator 8 through contact 7r of a transmission/reception switch 7 so as to be converted into first intermediate frequency fR1 of 248.3 MHz. Then, the selectivity of the converted signal is raised by a first intermediate frequency band-pass filter 9, followed by being amplified by a first intermediate frequency amplifier 10. Then, the amplified signal is, by a converter 11, mixed with second local oscillation frequency fL2 of 259.1 MHz from a second local oscillator 12 so as to be converted into second intermediate frequency fR2 of 10.8 MHz. Then, the selectivity of the converted signal is raised by a second intermediate frequency band-pass filter 15, and then demodulated by a demodulator 16.
When a signal is transmitted, a carrier-wave from an oscillator 17 having a frequency of 248.3 MHz is digital-modulated with I and Q signals by a modulator 19. The modulated signal is amplified by an intermediate transmission frequency amplifier 20. Then, the selectivity of the amplified signal is raised by an intermediate transmission frequency band-pass filter 21. And then, by a converter 22, the signal is mixed with first local frequency fL1 of 1646.85 to 1669.65 MHz supplied from the first local oscillator 8 through contact 7t of the transmission/reception switch 7 so as to be converted into high-frequency signal fT which is the same frequency as that used when a signal is received. The selectivity of the high-frequency signal fT is raised by a high-frequency band-pass filter 23, and then amplified by a high-frequency amplifier 24 and a high-frequency power amplifier 25, followed by being allowed to pass through contact 2t of the antenna switch 2. Then, the selectivity of the amplified signal is raised by the high-frequency band-pass filter 3, followed by being transmitted from an antenna 1.
The reception and transmission is switched such that the antenna switch 2 and the transmission/reception switch 7 are switched at a period, which is considerably shorter than a voice signal period, so as to time-divide the transmission and reception. As a result, simultaneous transmission and reception can be performed.
A conventional TDMA wireless unit and employing the FDD system to separate transmission and reception from each other will now be described with reference to the drawings. FIG. 8 is a block diagram showing a conventional TDMA wireless unit adapted to the FDD system. Referring to FIG. 8, when a signal is received, a high-frequency signal received through an antenna 1 is allowed to pass through an antenna switch 2 connected to a terminal 2r so that reception frequency fR of 801 MHz to 826 MHz for the subject station is selected by a high-frequency band-pass filter 3, followed by being received by a high-frequency amplifier 4 so as to be amplified. Then, the selectivity of the amplified signal is further raised by a high-frequency band-pass filter 5, followed by being mixed, by a converter 6, with first local oscillation frequency fL1 of 680 MHz to 696 MHz from a first local oscillator 8 through contact 7r of a transmission/reception switch 7 so as to be converted into first intermediate frequency fR1 of 130 MHz. The selectivity of the converted signal is raised by a first intermediate frequency band-pass filter 9, and then amplified by a first intermediate amplifier 10. Then, the amplified signal is, by a converter 11, mixed with second local oscillation frequency fL2 of 129.55 MHz from a second local oscillator 12 so as to be converted into second intermediate frequency fR2 of 450 kHz, and the selectivity of the converted signal is raised by a second intermediate frequency band-pass filter 15. Then, the signal is demodulated by a demodulator 16.
When a signal is transmitted, an output from a carrier wave oscillator 17 for generating carrier wave frequency fL of 260 MHz, which is different from the first intermediate frequency fR1, is, by a modulator 19, digital-modulated with I and Q signals so that modulation wave having an intermediate transmission frequency fT1 is generated. The intermediate transmission frequency fT1 is amplified by an intermediate transmission frequency amplifier 20. The selectivity of the amplified signal is raised by an intermediate transmission frequency band-pass filter 21. And then, by a converter 22, the signal is mixed with the first local frequency fL1 supplied from the first local oscillator 8 through contact 7t of the transmission/reception switch 7 so as to be converted into a high-frequency signal having transmission frequency fT of 940 MHz to 956 MHz which is the frequency of the subject station. Then, the selectivity of the high-frequency signal is raised by a high-frequency band-pass filter 23, followed by being amplified by a high-frequency amplifier 24 and a high-frequency power amplifier 25. Then, selectivity of the amplified signal is raised by a high-frequency band-pass filter 26, followed by being allowed to pass through a contact 2t of the antenna switch 2 so as to be transmitted from the antenna 1.
Similarly to the structure shown in FIG. 7, the reception and transmission is switched such that the antenna switch 2 and the transmission/reception switch 7 are switched at a period shorter than a voice signal so as to switch the transmission and reception frequencies. As a result, simultaneous transmission and reception can be performed.
A dual mode wireless unit which integrally accommodates the TDD system shown in FIG. 7 and the FDD system shown in FIG. 8 will now be described. FIG. 9 is a block diagram showing a conventional dual mode wireless unit. Referring to FIG. 9, the block diagram of TDD system shown in FIG. 7 and that of the FDD system shown in FIG. 8 are combined to each other. Moreover, a mode switch 28 is disposed among the antenna 1 and respective antenna terminals. The same elements as those shown in FIGS. 7 and 8 are given the same reference numerals and they are omitted from detailed description. The frequencies employed in each section shown in FIG. 9 are similar to those employed in the structures shown in FIGS. 7 and 8.
However, as can be understood from the descriptions of the conventional structures, the TDD system shown in FIG. 7 and the FDD system shown in FIG. 8 must be provided with the first local oscillator 8, the second local oscillator 12 and the carrier oscillator 17. The dual mode wireless unit shown in FIG. 9 involves a complicated frequency relationship and has a structure formed by simply combining the circuits employed in the structures shown in FIGS. 7 and 8. Thus, the number of the variable oscillators is the total of all oscillators shown in FIGS. 7 and 8. As a result, there arises a problem in that the number of the oscillators is too large and the circuit structure cannot be simplified.
In recent years, research and development of mobile telephones have been performed energetically, thus resulting in systems operated in a variety of frequency bands. Accordingly, also the wireless section of a wireless unit must treat signals in a plurality of frequency bands by the same circuit thereof. Among the foregoing circuits, the band-pass filter and frequency branching filter (combiner), which are important circuit elements in the wireless circuit encounter a variety of problems in treating a plurality of frequency bands.
Referring to the drawings, a conventional two-frequency band-pass filter with two frequency pass bands will now be described. FIG. 25 is a circuit diagram showing an essential portion of the conventional two-frequency band-pass filter. Referring to FIG. 25, reference numeral 161 represents a first band-pass filter with a center frequency of 950 MHz, and 162 represents a second band-pass filter with a center frequency of 1.9 GHz. A common input terminal 164, a common output terminal 165 and input and output terminals of the foregoing filters are connected to one another by filter switches 163. By synchronizing the foregoing switches 163 and by switching to the first filter or the second filter, the overall band allowed to pass through can be switched.
A conventional two-frequency branching filter will now be described. FIG. 26 is a circuit diagram showing an essential portion of a conventional two-frequency branching filter. Referring to FIG. 26, reference numeral 171 represents a first band-pass filter with a center frequency of 950 MHz, and 172 represents a second band-pass filter with a center frequency of 1.9 GHz. By causing an output switch 173 to switch a common input terminal 174 and input terminals of the foregoing filters, a frequency component of 950 MHz can be obtained at a first output terminal 175 and a frequency component of 1.9 GHz can be obtained at a second output terminal 176. By switching input and output, a two-frequency combiner can be structured.
However, the foregoing conventional structures results in both of the two-frequency band-pass filter and the two-frequency branching filter (combiner) being required to use control signals for the switches. Moreover, there is a risk that the loss of the switch deteriorates the overall insertion loss characteristic.
In recent years a voltage controlled oscillator (hereinafter abbreviated as a "VCO") capable of arbitrarily varying the frequency by changing voltage to be applied to a varactor diode has been employed in a variety of circuits, for example, a PLL. In particular, wireless units of a type using a plurality of frequency bands have widely used a VCO with controllable frequency band which can be used across at least two frequency bands.
Referring to the drawings, a conventional VCO with controllable frequency band capable of operating two frequency bands will now be described. FIG. 34 is a block diagram showing a conventional VCO with controllable frequency band. Referring to FIG. 34, the VCO with controllable frequency band comprises a VCO 391 (VCO1) for oscillating within the range of a first frequency band and a VCO 392 (VCO2) for oscillating within the range of a second frequency band. The VCO1 and VCO2 respectively are caused to oscillate in the corresponding bands, and then either of the oscillation outputs of the frequency bands is selected by a switch 393 so as to be conducted to the output terminal.
However, the foregoing conventional VCO with controllable frequency band is required to have a VCO at each desired frequency band. Since the time division multiple access FDD/TDD dual mode wireless unit is adapted to different transmission and reception frequencies in each mode, the frequency bands of the first and second local oscillator frequencies must be changed. Thus, the time division multiple access FDD/TDD dual mode wireless unit must be provided with the VCOs for the desired frequency bands. Thus, the size of the circuit and a required space are enlarged excessively while the cost being enlarged unsatisfactorily.
In recent years, flows of signals in a high-frequency circuit have been switched by using a switch device, such as a field-effect transistor. A conventional two-terminal to two-common-terminal matrix switch for forming one signal flow between two terminals and two common terminals will now be described with reference to a circuit diagram shown in FIG. 40.
A First terminal RF1 is connected to drains of two field-effect transistors (hereinafter abbreviated as "FET") Q11 and Q13. A Second terminal RF2 is connected to drains of two FETs Q12 and Q14. Sources of the two FETs Q13 and Q14 are joined together so as to be connected sources of FETs Q23 and Q24.
The drain of the FET Q23 and that of FET Q21 are connected to a first common terminal RFCOM1. The drain of the FET Q24 and that of the FET Q22 are connected to a second common terminal RFCOM2. The source of each of transistors Q11, Q12, Q21 and Q22 is grounded. A first control terminal Vcont1 is, through resistors R32 and R33, connected to the gate of the FET Q12 and that of the FET Q13. The first control Vcont1 is, through an invertor Inv1 and resistors R31 and R34, connected to the gate of the FET Q11 and that of the FET Q14.
A second control terminal Vcont 2 is, through resistors R36 and R37, connected to the gate of the FET Q22 and that of the FET Q23. The second control terminal Vcont2 is, through an invertor Inv2 and resistors R35 and R38, connected to the gate of the FET Q21 and that of the FET Q24.
The operation of the two-terminal to two-common-terminal matrix switch having the foregoing structure will now be described with reference to FIG. 41, which is a circuit equivalent to that shown in FIG. 40 and Table 1 showing the relationship between application of control voltage and the operation of the circuit.
TABLE 1 ______________________________________ Vcont1 Vcont2 H L ______________________________________ H RF1 .rarw..fwdarw. RFCOM1 RF2 .rarw..fwdarw. RFCOM2 L RF1 .rarw..fwdarw. RFCOM2 RF2 .rarw..fwdarw. RFCOM1 ______________________________________
As shown in Table 1, high level (H) or low level (L) potential is supplied from the first and second control terminals Vcont1 and Vcont2 as control voltage. In a case where both of the Vcont 1 and Vcont 2 are high level, an input signal supplied from the first terminal RF1 is, as shown in FIG. 41, conducted to the first common terminal RFCOM1 because the transistors Q13 and Q23 have been turned on because a FET is generally turned on when the potential of the gate is high and the transistors Q11, Q14, Q21 and Q24 have been turned off by the invertors Inv1 and Inv2. A signal from the second terminal RF2 is grounded because the transistor Q12 has been turned on and the transistor Q14 has been turned off and, therefore, the signal cannot be transmitted to another common terminal. When the potentials of both of the Vcont1 and Vcont2 are low, a reverse relationship to that shown in FIG. 41 is held in which the signal from the second terminal RF2 is conducted to the second control terminal RFCOM2 because the transistors Q14 and Q24 have been turned on and the transistors Q12, Q13, Q22 and Q23 have been turned off. An input signal from the first terminal RF1 is grounded because the transistor Q11 has been turned on and the transistor Q13 has been turned off. Thus, the signal cannot be transmitted to another control terminal.
Similarly, in the case where the potentials of the Vcont1 and Vcont2 are L and H and in the case where the same are H and L, the signal can be conducted as shown in Table 1. As a result, the operation as the two-terminal to two-common-terminal matrix switch is performed similar to the equivalent circuit shown in FIG. 42 in which the connection is independently established in only one set consisting of either of the two terminals and either of the two control terminals. The foregoing flow of the signal may be inverted.
However, the foregoing conventional two-terminal to two-common-terminal matrix switch having the foregoing structure requires 8 transistors arranged as shown in FIG. 40, thus causing the number of resistors to be enlarged. Thus, the structure of the circuit becomes too complicated. If the common terminals are intended to be increased, the number of the transistors increases inevitably and, therefore, control becomes too complicated. Since two FETs are, in series, disposed in a path from the input terminal to the common terminal of the output terminal, an excessive signal transmission loss takes place.